Effects of Rotation, Tillage, and Fumigation on Premature Dying of Soybeans. R. H. Von Qualen, Graduate Research Assistant, Botany and Plant Pathology Department, Purdue University, West Lafayette, IN 47907. T. S. Abney, D. M. Huber, and M. M. Schreiber. USDA, ARS Plant Pathologist, Professor, and USDA, ARS Agronomist, Botany and Plant Pathology Department, Purdue University, West Lafayette, IN 47907. Plant Dis. 73:740-744. Accepted for publication 17 February 1989. This article is in the public domain and not copyrightable. It may be freely reprinted with customary crediting of the source. The American Phytopathological Society, 1989. DOI: 10.1094/PD-73-0740.

Premature dying of Miami soybeans was reduced by crop rotation and fumigation and increased with reduced tillage in the USDA ARS-Purdue Integrated Pest Management systems in 1985 and 1986. In 1985, symptoms of premature dying of soybean plants in central Indiana were similar to those reported for sudden death syndrome (SDS). Diaporthe spp. were consistently associated with plants dying at the R6 growth stage. These plants were shorter, had fewer nodes, and yielded less than plants that did not die prematurely. Premature dying was more extensive in a continuous soybean (S-S) cropping than in a corn-soybean (C-S) rotation and was least extensive in a wheat-corn-soybean (W-C-S) rotation (11, 6, and 2%, respectively). Yields of the S-S, C-S, and W-C-S rotations were 2,650, 3,047, and 3,262 kg/ha, respectively. The dying pattern paralleled yield reductions. Soil fumigation with metham (sodium methyldithiocarbamate) reduced the incidence of SDS and increased yield both years. In 1986, symptoms of SDS and brown stem rot occurred. Phialophora and Diaporthe were isolated from prematurely dying plants. Classical pith discoloration symptoms caused by P. gregata were predominant. More plants died prematurely in the S-S rotation (11%) than in the W-C-S rotation (2%), and fumigation of soil with metham reduced premature dying from an average of 5 to 3%. Premature dying in the S-S rotation was consistently higher in no-tillage plots than in either conventionally tilled or chisel-plowed plots both years.